The present invention relates to a linear actuator which can precise carry out velocity and positioning control.
Until now, there have been means for utilizing a motor or a linear motor, or means for utilizing fine actuators, such as piezoelectric elements, to accomplish precise linear drive.
FIG. 1 is a summarized cross-sectional view of one example of a means for indirectly obtaining a linear driving force utilizing a motor. A rotational driving force obtained by a motor 1 is transferred to a ball screw 5 through pulleys 2 and 3 and a belt 4, converted into the linear driving force by a ball screw nut 6 into which the ball screw 5 is screwed, and linearly drives a driving base 8 through a supporting bracket 7.
FIG. 2 is a summarized cross-sectional view of one example of a means for directly obtaining a linear driving force utilizing a linear motor. A slider 131 of a linear motor 13 is fixed to a driving base 11 through a supporting bracket 12 and the driving base 11 is linearly driven by the linear driving force of the linear motor 13.
FIG. 3 is a summarized cross-sectional view of one example of a means for directly obtaining a linear driving force utilizing fine actuators such as piezoelectric elements. Both ends of a cylindrical driving fine actuator 21 which can axially expand and contract are respectively fastened to side faces of fixing/separating fine actuators 22 and 23 like the fine actuator 21, and a rod-like driving base 24 is fastened to the side face of the fixing/separating fine actuator 22 so that its longitudinal axis is coincident with the direction of expansion and contraction of the driving fine actuator 21. In the actuator unit of such a structure, the driving base 24 runs through the side of a box-like supporting bracket 25, and the fixing/separating fine actuators 22 and 23 are housed in the supporting bracket 25 so that they support the inside face of the supporting bracket 25 in an expansion state and come apart from the inside face of the supporting bracket 25 in a contraction state.
FIG. 4 is a block diagram of one example of a driving apparatus of the linear driving means shown in FIG. 3. A position controlling circuit 414 inputs a velocity signal VS and outputs expansion/contraction signals SS3, SS4 and SS5 to each of drives 433, 434 and 435. Each driver 433, 434 and 435 supplies each of the expansion/contraction signals SS3, SS4 and SS5 to the respective fine actuators 21, 22 and 23 after power amplifications. An example of each of the expansion/contraction signals and each of the driver's outputs is shown in the time chart in FIG. 5, and the velocity signal is in proportion to frequency of each of the expansion/contraction signals. Its operating sequence will be explained referring to the time chart shown in FIG. 5 as follows.